1. Field of the Invention
The present invention relates to a decoding apparatus for decoding coded data. More particularly, the invention relates to a decoding apparatus, a decoding control apparatus, and a decoding method for performing a noise reduction process upon decoding, as well as a program for causing a computer to execute the decoding method.
2. Description of the Related Art
There exist video compression coding schemes which, in digitally compressing a video signal, regard a plurality of pixels of the target video signal positioned horizontally and vertically contiguous to one another as one rectangular block and enable compression coding to be performed in units of that block. Such video compression coding schemes include standards such as MPEG-2 and H.264/AVC. The video signal compression-coded in units of the above-mentioned rectangular block by one of these compression coding schemes is decoded also in units of the block, whereby the original video signal is restored. According to MPEG-2, for example, the video data constituting the video signal is split into macro blocks each composed of eight lines by eight pixels amounting to 64 pixels. The video data is subjected to orthogonal transformation such as discrete cosine transform (DCT) in unit of such a macro block. The video data is thus transformed into frequency components (DCT coefficients) which are coded to compress the video data.
The compression coding and decoding schemes outlined above reduce code amount by significantly abbreviating radio frequency components when performing the step of quantizing the coefficient values following orthogonal transformation, thereby enhancing coding efficiency (compression rate). However, if the step of quantization is reinforced excessively, the quantization error stemming from the abbreviated radio frequency components may degrade image quality in the decoded video data.
In connection with image quality degradation, so-called mosquito noise or ringing noise is known to appear particularly on the periphery of an image edge, the noise being dispersed around the edge. The mosquito noise is generated by lack of information near the edge due to reductions of radio frequency components in the quantization process. Electronic information devices (e.g., see Japanese Patent Laid-Open No. 2007-13398, FIG. 1) have been proposed to remove such mosquito noise. The proposed devices illustratively have a post-filter for digital video processing positioned downstream of the decoder.